1. Field of the Invention
The present invention relates to a structure allowing for detection of a load applied to a vehicle seat. In particular, the invention is directed to load detection structure of such a type wherein a longitudinally elongated strain plate member is provided, which extends along the fore-and-aft direction of the vehicle seat and wherein a load detection device having a strain gauge is provided under the seat such that the strain gauge detects an amount of deflection of the strain plate member which is caused by a load applied to the seat and gives a numerical data indicative of the deflection amount.
2. Description of Prior Art
Various automatically controlled functions and mechanisms have been increasingly incorporated in vehicle or automobiles, including safety devices such as air bags for protecting passengers against a great impact automatically in response to a collision. With such automated control innovations, there have been also found technical improvements to a passenger detection system for detecting the presence and absence of a passenger or driver in a seat of vehicle in advance before actuating or stopping the associated mechanical elements to automatically control various functions and mechanisms built in the seat.
Normally, the passenger detection system or a load detection structure employs sensors which can detect a load in terms of presence and absence of passenger on a seat, and recent high-tech control technology has developed sensors capable of detecting a degree of load whether the passenger is an adult or a child as with air bag control system for instance.
In such load detection structure, as disclosed from the Japanese Laid-Open Patent Publication No. 11-304579, a strain plate element and a strain gauge are employed, with such an arrangement that an amount of deflection of the strain plate element, which is caused by a load applied thereto from a seat is detected by the strain gauge. In view of the fact that the load is applied downwardly to the strain plate element which is in turn resiliently deflected, it is a normal practice to provide the strain plate element under the seat.
But, in most cases, a slide rail device is provided under the seat to allow for free forward and backward movement of the seat. Further, the abovementioned Pub. No. 11-304579 is found defective in that its link mechanism and pivoted arm are complicated in structure and further they occupy much of space heightwise between the seat and slide rail device, which results in the seat becoming large vertically in size and increasing its weight. Therefore, providing this kind of load detection structure between the slide rail device and seat will inevitably lead to an undesired increase in height of the seat. In fact, there is a strong demand among many technical peoples for a very thin structure in this particular kind of seat to avoid such increase in height of seat.
Also, the strain plate element is vulnerable to an excessive great load which is abruptly and directly applied thereto in such an emergency case as a collision or the like. That is, when applied by the excessive great load, the strain plate element is deflected to an excessive degree and may be broken. To solve the problem, there have been various conventional sorts of limit elements for limiting vertical deflection of the strain plate element. But, many of those conventional limit elements are relatively large in size because they require such a relatively massive parts as bolts, brackets and the like. This, after all, will lead to an undesirably large size of the load detection structure with many parts and complicated structure.
In view of the above-stated drawbacks, it is therefore a primary purpose of the present invention to provide an improved load detection structure arranged at a slide rail device of a vehicle seat, which is greatly simplified in structure with reduced number of constituent element and effective in avoiding undesired increase in height of the seat.
In order to accomplish such purpose, the load detection structure in accordance with the present invention includes a load detection means for detecting a load applied from an occupant on a vehicle seat and the load detection means is basically comprised of:
a strain plate element having an elongated body extending in the longitudinal direction thereof, an upper flat surface, and a lower flat surface, the strain plate element having a rigid yet elastically deformable property and including, defined therein, a first end portion, a second end portion, an intermediate portion between the first and second end portions, and a hinge half portion formed integrally in and transversely of the second end portion, said hinge half portion thereby having a half through-bore of a semi-circular cross-section defined therein;
a strain gauge means fixedly attached to the intermediate portion of the strain plate element;
a first reinforcement plate fixed by at least one pin on the upper flat surface of the strain plate element at a point corresponding to the first end portion;
a second reinforcement plate fixed by such at least one pin on the lower flat surface of strain plate element at a point corresponding to the fist end portion;
the at least one pin being at one end thereof fixed to a bottom side of said vehicle seat;
a hinge plate having a half hinge portion so formed therein as to have a half through-bore of a semi-circular cross-section defined therein, the hinge plate being fixed to the strain plate element at the second end portion so that the half hinge portion of the hinge plate is aligned with the half hinge portion of said strain plate element, thereby defining a hinge through-bore of circular cross-section therein;
wherein a hinge pin is inserted in the hinge through-bore and securely provided in the support leg means, whereby the strain plate element is rotatably journalled by the hinge pin within the support leg means, and wherein, when a downward load is applied to the vehicle seat in a vertical direction, the first end portion of the strain plate element is displaced in a generally rectilinear downward direction, while at the same time, the second end portion of the strain plate element is rotated about the hinge pin, whereupon a difference is caused in movement and direction between the first and second end portion, thereby causing deflection of the intermediate portion, and, in response thereto, the strain gauge means detects an amount of the deflection and emits a corresponding value indicative of an amount of the load.
Accordingly, the hinge portion in which the strain plate element is rotated is effectively made small heightwise in thickness within the support leg means without requiring another thick support elements. Thus, the load detection structure can be kept thin in heightwise, thereby avoiding undesired increase in height of the seat.
In one aspect of the present invention, a stopper means is provided for limiting vertical movement of the first end portion of stain plate element and the stopper means comprises an upper stopper piece and a lower stopper piece, wherein the upper and lower stopper pieces are formed in each of a pair of vertical walls of the support leg means by cutting and bending a corresponding local area of each of those two vertical walls in a direction inwardly of the support leg means. The first end portion of strain plate element is normally positioned between the upper and lower stopper pieces, such that one limited clearance is given between the upper stopper piece and the first end portion, while another limited clearance is given between the lower stopper piece and the first end portion.
Other features and advantages will become apparent from reading of descriptions hereinafter, with reference to the annexed drawings.